Recovery of condensable products from gaseous mixtures



United States Patent Int. Cl. F25j 3/06 US. C]. 62-23 16 Claims ABSTRACTOF THE DISCLOSURE A process is disclosed for recovering liquid productsfrom a gaseous mixture. The mixture is cooled initially bycountercurrent heat exchange with separated constituents of precedingportions of the same mixture and a recycled refrigerant. This initialcooling condenses some of the constituents. The liquid product thusformed is separated from the gas. The gas is then expanded to a lowerpressure while doing mechanical work to cool it to a still lowertemperature and condense more liquid products, which are combined withthe first liquid products obtained to provide a cold liquid productstream and a cold gas stream. The cold product stream and a cold liquidrefrigerant stream are combined and passed in heat exchange relationshipwith the gaseous feed stream to provide the initial cooling describedabove by partially vaporizing the combined liquid product andrefrigerant stream. The vaporized portion of the combined liquid streamis separated from the remaining liquid and compressed with the powerfrom the expanding of the gaseous feed stream as described above. Thecompressed vapor is cooled to condense some of it at substantiallyambient temperature and to remove the latent vheat of vaporization ithad picked up in the heat exchanger. The partially condensed stream isrecycled through the heat exchanger to condense additional vapor andthereby provide a liquid stream. This liquid stream is expanded,combined with the liquid product stream and passed through the heatexchanger as a refrigerant to cool the incoming feed stream.

This application is a continuation-in-part of our prior copendingapplication Ser. No. 445,113, filed Apr. 2, 1965, now abandoned.

This invention relates to improvements in processes for the recovery ofliquid products from a gaseous mixture. It is particularly useful in therecovery of ethane and heavier hydrocarbons from a stream of naturalgas, but is not limited to such use.

In conventional cryogenic processes for the separation of a liquidproduct from a gaseous mixture it is customary to pass a feed stream ofthe gaseous mixture through indirect heat exchange with cold productspreviously separated from the gaseous mixture to cool the feed stream toor near to condensation temperature of its heaviest condensiblecomponents. The feed stream, or a portion of it, is then expandedthrough an expansion engine to cool it further. The refrigerationgenerated in the expansion engine has been used to condense a portion ofthe expanded stream or a side stream of the unexpanded gas mixture byindirect heat exchange, and the liquid condensate obtained is oftensubjected to one of many fractional separation treatments for furtherresolution of the mixture. The separated cold constituents usually arereturned through indirect heat exchange with the incoming stream ofgaseous mixture and are then withdrawn as products.

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Such processes require large quantities of low temperature refrigerationto absorb the latent heat of vaporization of the product. If the coldliquid product stream is used to absorb this latent heat of vaporizationof the incoming feed stream, not only will all of the lighter and morevolatile hydrocarbons in the product stream be vaporized, but most ofthe heavier hydrocarbons as well.

It is an object of this invention to provide a process for the recoveryof a liquid product from a gaseous mixture in which very littlevaporization of the liquid product occurs as it passes in heat exchangerelationship with the incoming gas stream.

It is another object of this invention to provide a process for therecovery of a liquid product from a gaseous mixture in which arefrigerant comprised of the lighter hydrocarbons in accumulated in thesystem and recycled with the cold liquid product obtained from the feedstream to vaporize and absorb the latent heat of vaporization of thecondensable constituents of the feed stream.

Another object is to provide a process of the above type in whichexpansion of the gas furnishes all the power for the low temperaturerefrigeration required.

Another object is to provide a process of the above type wherein a largepart of the vaporization latent heat of the product is removed atsubstantially ambient atmospheric or similar readily maintainabletemperature.

Another object is to provide a process of the above type which resultsin a liquid product low in gaseous constituents.

Another object is to provide a process of the above type in which theapparatus used may be simple in construction.

Highest efiiciency in operation of a process involving a heat exchangerthrough which streams of gases and liquids are passed countercurrentlyis known to require that the temperature differential betweencountercurrent streams be small; and if the heat exchanger is not to beexcessively large, this temperature difference should be substantiallyuniform at all locations along their countercurrent paths in the heatexchanger, that is, the temperatures of the streams should not convergeor diverge as they approach the warm or cold end of the heat exchanger.Lack of reasonably uniform temperature differential has increased theoperating cost of prior processes for recovery of liquid from gaseousmixtures.

Therefore, another object is to provide a process of the above type inwhich a main heat exchanger may be used for cooling an incoming feedstream of a gaseous mixture by product streams in which substantiallyuniform temperature differential between the streams at consecutivelocations in the heat exchanger is easily maintained.

Another object is to provide a process of the above type in whichtemperature differences between the feed stream of gaseous mixture andproduct streams are controllable to prevent the temperatures of thestreams from converging or diverging.

Another object is to provide such process in which a single expander anda single compressor may be used, and in which the flash gas is returnedto the process.

Still another object is to provide such process which is inexpensive inoperation, and which can be made substantially automatic.

Another object is to provide a process utilizing an expansion engineloaded with a compressor in which a portion of the compression energyacts to operate a refrigeration system based on liquefiable componentsin the com pressed stream to augment the refrigeration for carrying outthe process.

Other objects and advantages will become apparent to those skilled inthe art from consideration of the following detailed description and theattached drawing.

In the attached drawing the single figure is a schematic flow diagram ofa process involving the principles of my invention.

The following detailed description is directed to a process forseparating ethane and higher hydrocarbons from a feed stream of naturalgas containing the same, but it is to be understood that it isapplicable to a great many gaseous mixtures which contain componentsthat are liquefied on cooling and application of pressure.

Referring to the drawing, an incoming feed stream of a gaseous mixturecontaining liquefiable components, as, for example, a stream of naturalgas containing ethane and/or higher hydrocarbons, such as propane and/orbutane, enters under pressure through line 1 at a rate of flowcontrolled by valve 2 and passes through pass b in main heat exchanger 3where it is cooled to a lower temperature, and is preferably partiallycondensed to produce a large portion of crude liquid products. When thestream is natural gas containing ethane and higher hydrocarbons, it mayenter exchanger 3 at substantially well pressure, if desired.

The partially condensed feed stream is withdrawn from heat exchanger 3by line 4 and is discharged into separator 5 where the liquid condensedin the heat exchanger is disengaged from residual gas. A portion of thedisengaged gas may be returned through line 6 and pass e through theheat exchanger 3 and discharged as a dry gaseous product through line 7if there is more gas being supplied to the system than is required tosupply refrigeration and power to the system by expansion as describedbelow. Frequently, the return of gas through line 6 and heat exchangerpass e is not necessary.

The remainder of the gas separated in a separator 5 is passed throughline 8 to an expansion engine, illustrated as turboexpander 9. Thegaseous stream is further cooled, additional liquid is condensedtherefrom, and power is generated by expanding the gaseous stream to alower pressure through the turboexpander. The liquid condensed in pass bof heat exchanger 3 and separated from the gas in separator 5, iswithdrawn from the separator and introduced into a cold gas streamcoming from a later described separator 16. This cold gas stream is richin constituents to be recovered as liquid.

The resulting combined two phase stream flows through conduit 17 andheat exchanger 18 where it is cooled still further, and into line 11, bywhich it is introduced into the low pressure and very cold eflluent fromthe turboexpander 9 flowing through line 12 to separator 13, where themixed liquid is disengaged from residual gas. The liquid recovered inseparator 13 is the crude liquid product and is at a very lowtemperature and at approximately the low pressure of the expandedeffluent from the turboexpander 9.

The residual gas withdrawn from separator 13 is the combined residue gasstream and is likewise at the very low temperature and low pressure ofthe eflluent from said turboexpander. This stream flows out through line14 which returns it to pass a of heat exchanger 3 where itsrefrigeration content is recovered by cooling the incoming stream offeed gas. The residual gas stream is withdrawn as a dry gas productthrough line 15.

The crude liquid product in separator 13 is withdrawn by line 19 and ispassed through heat exchanger 18 where its temperature is raisedsomewhat. This results in vaporization of some of the more volatilecomponents of the mixture, as for example methane and part of the ethanefrom a natural gas mixture, and at least partially strips the liquid ofsuch materials. The resulting two phase mixture passes into separator 21where the liquid and vapor are separated.

The liquid product that has been recovered from the gas flowing into thesystem is combined with a liquid stream of refrigerant flowing throughline 16a from separator 16 and the combined stream of liquid productsand refrigerant flows through pass c of heat exchanger 3. As will befurther explained below, the refrigerant employed comprises mostlylighter hydrocarbons that have been recovered and accumulated from theliquid products initially produced by the process and thus these lighterends will vaporize more readily then the liquid product, which containsa much higher percentage of heavier hydrocarbons. Thus, as the combinedstreams of refrigerant and liquid product pass through heat exchanger 3,substantially all the refrigerant will vaporize as it absorbs heat fromthe incoming feed stream of gas. Some of the lighter ends of the liquidproduct may vaporize also, but this is held to a minimum. As thecombined streams leave the heat exchanger and pass into separator 28through line 27, the liquid product will still be substantially allliquid. The liquid product is separated from the vaporized refrigerantin separator 28 and collected in liquid product tank 32 through line 41.

The refrigerant, which was substantially all vaporized as it passedthrough the heat exchanger, will leave separator 28 as a gas throughline 29, join the vapors separated from the liquid product in separator21, and travel through line 33 to the intake of compressor 23. On theway this stream will also be joined by the vapors coming off of storagetank 32. Pressure regulator 25 in line 33 maintains a given pressure onseparator 28 and the liquid product and refrigertant as they passthrough the heat exchanger. By controlling the pressure in the heatexchanger, the amount of liquid that is vaporized therein can becontrolled and thus the pressure regulator acts as a control of thetemperature in the heat exchanger.

Vapors flowing through line 33 are compressed by compressor 23, which ispowered by turboexpander 9. After being compressed to a relatively highpressure, the vapors are cooled in condenser 35, which may be cooled inany convenient fashion, as by water from a cooling tower which isintroduced to the condenser through line 36 and withdrawn through line37. Compressor 23 raises the pressure of the vapors sufficiently that asubstantial portion of the vapors will condense in condenser atsubstantially ambient temperature. Thus, the heat of vaporizationabsorbed by the refrigerant, as it is vaporized in heat exchanger 3, isremoved from the process by a conventional cooling tower operating at oraround ambient temperatures. This is a very economical way to removethis heat from the incoming gas stream.

The combined liquid and vapor flowing out of condenser 35 passes throughseparator 35a, where the liquid and vapors are separated. The vapor andliquid are still at relatively high pressures. The vapor separated fromthe liquid in separator 35a passes through line 3512, through backpressure valve 38, which maintains a given pressure on separator 35a,and then into line 39. The liquid in separator 35a travels through line42, through back pressure regulator valve 43, and rejoins the vapor inline 39 before passing back through heat exchanger 3 through pass d ofheat exchanger 3. Line 350 is also connected to separator 35a andpermits a portion of the liquid separated in separator 35a to be drawnoff through line 35c. This liquid is introduced into the liquid leg ofseparator 28 and returned to liquid product storage tank 31. Thispermits a control on the amount of refrigerant being circulated in thesystem and there may be periods when no liquid is being withdrawn fromseparator 35a, particularly in the beginning when an inventory ofrefrigerant is being accumulated.

The refrigerant then flows through pass d of heat exchanger 3, is cooledby the refrigerant and liquid product stream flowing through pass 0 andthe cold gas flowing through pass a. This condenses more of the vaporsso that when the refrigerant stream reaches separator 16, it may well besubstantially all liquid. What remains as vapor is separated from therefrigerant at this point and passed back into the process through line16b, where it joins the liquid coming out of separator 5, is condensedsubsequently by the cold eflluent of turboexpander 9, and thus rejoinsthe liquid product stream. The liquid refrigerant is expanded throughvalve 160 to the lower pressure of line 22, which further cools theliquid refrigerant before it joins the liquid product and returnsthrough pass 0 of the heat exchanger.

Since the lighter hydrocarbons will more readily vaporize than theheavier, when the process is initially started up substantially all ofthe liquid product will be vaporized in pass c and recycled back throughthe compressor, heat exchanger, separator 16, etc., and used as arefrigerant. As the process continues, an inventory of refrigerant willbe accumulated until the system is balanced, with sufficient refrigerantbeing recycled to provide the cooling required. Further, during theaccumulation of this refrigerant, less and less of the heavierhydrocarbons in the liquid product stream coming out of separator 21will be vaporized in the heat exchanger. This results because thelighter hydrocarbon content of the refrigerant will increase until itconsists of substantially all lighter hydrocarbons. The refrigerant thenwill more readily vaporize and absorb the latent heat of vaporizationthat is given up by the incoming feed stream.

It is estimated that one half pound of refrigerant will be required forevery two pounds of feed gas that is introduced into the system. Everytwo pounds of gas, however, will only produce about A of a pound ofliquid product. From this it can be seen that the liquid product streamis relatively small compared to the refrigerant that is circulatedthrough pass 0. But with applicants process of recombining therefrigerant and the liquid product upstream prior to its being broughtback to pass 0 of the heat exchanger, most of the liquid product iscollected as liquid, in liquid product tank 32, which is what isdesired.

Heat exchanger 35 is not restricted to cooling with cooling water orair. It might be a coil in the warm end of heat exchanger 3, or in line31, or elsewhere. It would still be advantageous to carry out theprocess if heat exchanger 35 is at a higher temperature than that atwhich the liquid is being evaporated, even though considerably lowerthan ambient atmospheric.

Another important feature of the process described above lies in itscapability of being controlled in a way to adjust temperaturedifferences in heat exchanger 3 to correct for either divergence orconvergence of temperature difference. For example the vapor in therefrigerant stream entering pass d of the heat exchanger may condense ata temperature higher than that necessary to maintain a uniformtemperature difference between the streams in the heat exchanger. Thiscan be prevented by admitting a small amount of the incoming feed streamof gaseous mixture from line 1 through line 40 and valve 40a. Thepresence of a minor proportion of the gaseous mixture withdrawn from thefeed stream in line 39 and pass d of the heat exchanger reduces thepartial pressure of condensing constituents in pass a so that theycondense at a lower temperature, thereby liberating latent heat in passd at a lower temperature and nearer the cold end of the heat exchanger,and adjusting the temperature difference divergence.

Under certain circumstances of feed gas composition the incoming feedstream of gaseous mixture may require further cooling after it passesthrough pass b of heat exchanger 3 and before going to the turboexpander9. Under these circumstances it is preferred that the feed stream bepassed through an auxiliary heat exchanger 46 in countercurrent heatexchange with cold gas from separator 13 flowing through line 14,

From the foregoing, it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the process and method.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawing is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1s:

1. A process for separating a liquid product from a gaseous mixture at arelatively high pressure comprising the steps of separating a productstream from the gaseous mixture as a cold liquid leaving a gaseousresidue, reducing the pressure of the product stream and combining thecold product stream with a cold stream of recycled liquid refrigerant,passing the combined liquid product and refrigerant stream through aheat exchanger to cool the incoming gaseous stream by vaporizing asubstantial amount of the refrigerant and a portion of the productstream, separating the vapor so produced from the remaining liquidproduct, compressing the vapor, cooling the compressed vapor to condensea portion thereof, returning the vapor and condensate through the heatexchanger together to condense more of the vapor, separating thecondensate from the vapor, and reducing the pressure of the condensateto provide the cool stream of liquid refrigerant for combining with theproduct stream prior to passing the product stream through the heatexchanger.

2. The process of claim 1 further provided with the step of periodicallyremoving a portion of the condensate produced when the vapor isinitially cooled following compression to keep the amount of refrigerantbeing recycled substantially constant.

3. The process of claim 1 in which the cold product stream is obtainedby initially cooling the gaseous stream by the cold product andrefrigerant stream passing through the heat exchanger, separating thecondensate thus formed from the gaseous stream, work expanding thegaseous stream to further cool the gaseous stream to condense additionalliquid therefrom and to generate power for compressing the vapor fromthe refrigerant mixing the liquid first condensed and separated from thegaseous stream with the liquid condensed from the work expansion and theexpanded gas at the lower pressure, separating the gas from the liquidto provide a cold liquid product stream and a cold gas stream forpassing through the heat exchanger.

4. The process of claim 3 in which the vapor remaining in the recycledrefrigerant is separated therefrom and combined with the first condensedliquid before the liquid refrigerant is combined with the cold liquidproduct stream.

5. A process for recovery of a liquid product from a gaseous mixturecontaining a material which is liquefied on cooling comprising the stepsof passing a feed stream of said gaseous mixture under a relatively highpressure through indirect heat exchange with separate streams of coldgas and liquid previously recovered from advance portions of saidgaseous mixture; thereby cooling the feed stream sufficiently tocondense liquid therefrom; separating condensed liquid from the gaseousstream; further cooling the separated gaseous stream to condense additional liquid therefrom and to generate power by expanding the gaseousstream to a lower pressure through an expansion engine; mixing theliquid first condensed, additional liquid condensed, and expanded gas atsaid lower pressure; separating the expanded gas from the mixedcondensed liquid; returning streams of the cold expanded gas and mixedliquid separately in indirect heat exchange with later portions of saidfeed stream of gaseous mixture; maintaining the stream of mixed liquidat said lower pressure during said heat exchange; vaporizing at least apart of the mixed liquid by absorbing heat from the feed stream ofgaseous mixture; withdrawing the resulting vapor from heat exchange;compressing the vapor to a pressure higher than that at which it wasevaporated with power generated by expansion of said gaseous stream insaid expansion engine; recondensing at least a part of the compressedvapor to liquid at approximately ambient atmospheric temperature;withdrawing a large part of the resulting condensate as a liquid productand recycling the remainder into said stream of mixed liquid returningto said indirect heat exchange to act as a refrigerant in maintainingthe temperature range of said indirect heat exchange at a desired value.

6. The process of claim wherein the feed stream is a stream of naturalgas containing hydrocarbons in the range of ethane, propane, butane andheavier hydrocarbons.

7. The process of claim 6 wherein the mixed liquid is warmed andpartially vaporized by heat exchange with the liquid first condensedfrom the feed stream, the liquid product is held in a container, vaporis evolved from said liquid product, and prior to the compression stepsaid last-mentioned evolved vapor is mixed with vapor of mixed liquidwithdrawn from heat exchange with the feed stream and with vapor fromsaid partial vaporization of mixed liquid.

8. A process for recovery of a liquid product from a gaseous mixturecontaining a material which is liquefied on cooling comprising the stepsof passing a feed stream of said gaseous mixture under a relatively highpressure through indirect heat exchange with separate streams of coldgas and liquid previously recovered from advance portions of saidgaseous mixture; thereby cooling the feed stream sufficiently tocondense liquid therefrom; separating condensed liquid from the gaseousstream; further cooling the separated gaseous stream, condensingadditional liquid therefrom and generating power by expanding thegaseous stream to a lower pressure through an expansion engine; mixingthe liquid first condensed, additional liquid condensed, and expandedgas at said lower pressure; separating the expanded gas from the mixedcon densed liquid; returning the stream of cold expanded gas separatelyto indirect heat exchange with later portions of said feed stream ofgaseous mixture; passing the liquid first condensed through indirectheat exchange with said mixed condensed liquid prior to mixing theliquid first condensed with said additional liquid condensed andexpanded gas and thereby partially vaporizing the stream of mixed liquidby such heat exchange, separating the resulting vapor from the mixedliquid, returning the resulting mixed liquid residue to indirect heatexchange with the feed stream of gaseous mixture; maintaining the streamof mixed liquid at said lower pressure during said heat exchange;vaporizing at least a part of the mixed liquid by absorbing heat fromthe feed stream of gaseous mixture in such heat exchange; withdrawingthe resulting vapor from said heat exchange and mixing it with the vaporpreviously separated from said mixed liquids; compressing the vapormixture so produced to a pressure higher than that at which it wasevaporated with power generated by expansion of said gaseous stream insaid expansion engine; recondensing at least a part of the compressedvapor to liquid at approximately ambient atmospheric temperature; andwithdrawing a large part of the resulting condensate as a liquidproduct.

9. A process for separating a liquid product from a gaseous mixture at arelatively high pressure comprising the steps of separating a productstream from the gaseous mixture as a cold liquid leaving a gaseousresidue; reducing the pressure and evaporating a portion of the coldliquid product stream as it passes through a heat exchanger, therebyrecovering its refrigeration content at low temperature; expanding thegaseous residue to a relatively low pressure through an expansion engineto generate power and to provide additional liquid product'for theliquid product stream; compressing the portion of the cold liquidproduct stream that is evaporated as it passes through the heatexchanger to a pressure higher than said reduced lower pressure with thepower generated by the expansion engine, thereby raising its condensingtemperature; condensing part of the compressed portion to liquid at atemperature higher than that at which it was evaporated; separating saidcondensed liquid from said portion to provide a vapor recycle streamfrom said portion; passing said vapor recycle stream through said heatexchanger to be cooled by the liquid product stream to condense aportion of the vapor recycle stream; separating the condensed liquidfrom said vapor recycle stream after it passes through the heatexchanger, and combining said separated liquid with said cold liquidproduct stream before the cold liquid product stream enters the heatexchanger.

10. The process of claim 9 in which the said higher temperature at whichthe product is condensed is approximately ambient atmospherictemperature.

11. The process for recovery of a liquid product from a gaseous mixturecontaining a material which is liquefied on cooling comprising the stepsof passing a feed stream of said gaseous mixture under a relatively highpressure through heat exchange with separate streams of cold gas andliquid previously recovered from treatment of advance portions of saidgaseous mixture; thereby cooling the feed stream sufiiciently tocondense liquid therefrom at such relatively high pressure; separatingcondensed liquid from the gaseous stream to form cold gas and liquidstreams; condensing additional liquid for the cold liquid stream andgenerating power by expanding the gaseous stream from said relativelyhigh pressure to a lower pressure through an expansion engine; returningthe condensed liquid stream and expanded gaseous stream at such lowerpressure to indirect heat exchange with later portions of the feedstream to produce said initial cooling of the feed stream; vaporizing aportion of the liquid stream at low temperature by said indirect heatexchange; compressing said vapor to a pressure higher than said lowerpressure by power derived from expansion of said gaseous stream;condensing at least a part of the compressed vapor at approximatelyambient atmospheric temperature; separating the condensate formed bysaid compression to provide a vapor stream; recycling said vapor streamin indirect heat exchange with said separate streams of cold liquid andgas initially obtained from the gaseous mixture to re-cool the vapor andcondense a portion thereof thereby reclaiming at least a portion of theproduct previously vaporized when used as a refrigerant to cool theincoming feed stream, separating the condensed liquid product from saidvapor recycle stream and returning said liquid from the recycled vaporto said stream of cold liquid to act again as a refrigerant to cool saidincoming feed stream.

12. The process of claim 11 wherein the feed stream is a stream ofnatural gas containing hydrocarbons in the range of ethane, propane,butane and heavier hydrocarbons.

I13- In a process for the recovery of a liquid product from a gaseousmixture containing a material liquefied by a cooling under pressure inwhich a feed stream of the gaseous mixture is passed throughsimultaneous countercurrent indirect heat exchange with at least twocold product streams, at least one of said cold product streams beingsubstantially liquid, with a portion of said liquid product stream beingvaporized during said heat exchange to increase the heat absorbed fromsaid feed stream by the latent heat of vaporization required to vaporizesaid portion of the liquid product stream that is vaporized, thatimprovement which comprises maintaining a more uniform temperaturedifference between the feed stream and the cold product streams as theyflow countercurrently through the heat exchange by the steps consistingof separating a vapor recycle stream from the vaporized portion of theliquid product stream downstream of said heat exchange; passing saidvapor recycle stream concurrently with said feed stream through saidheat exchange to cool said vapor recycle stream sufiiciently to condensea portion thereof to thereby reduce the temperature difference betweenthe cold product streams and the feed stream; separating the liquid fromsaid cooled recycle stream, and returning said separated liquid to saidliquid product stream upstream of the heat exchange.

14. The process of claim 13 including the steps of compressing saidvaporized portion of theliquid product stream to a pressure whereinconstituents therein are easily condensed at a temperature higher thanthe temperature in said heat exchange, cooling said compressed vaporstream to condense said constituents, and separating the condensateformed from said vapor stream to form said vapor recycle stream.

'15. The process of claim 14 further including the step of re-combininga portion of the liquid condensed from said compressed vaporized portionwith the vapor recycle stream to cause the condensation of the vapor tooccur References Cited UNITED STATES PATENTS 2,685,180 8/1954 Schlitt62--30 3,205,669 9/1965 Grossmann 6223 3,212,277 10/ 1965 Harper 62-233,218,816 11/ 1965 Grenier 62-26 3,274,787 9/ 1966 Grenier et a1 6-2-263,292,381 12/ 1966 Bludworth 62 -26 NORMAN YUDKOFF, Primary Examiner 20A. F. PURCELL, Assistant Examiner us. 01. X.R. 62 -26, 38, 4o

